Traditional luminaires based on fluorescent lamps are more and more replaced by LED-based luminaires. Indeed, LEDs provide great freedom of design and energy advantages. However, by replacing a fluorescent lamp with one or more LEDs, the limited dimensions of this light source offer an extra design challenge because its concentrated brightness must be distributed on a larger surface in order to create an acceptable luminance which is not disturbing to the user.
Luminaires of the type described in the opening paragraph are known per se. They are used, inter alia, as luminaires for general lighting purposes, for example, for office or shop lighting, for example, shop window lighting or lighting of (transparent or semi-transparent) plates of glass or (transparent) synthetic resin on which items, for example, jewelry, are displayed. An alternative application is the use of such illumination systems tier illuminating advertising boards, billboards as display devices.
Such a luminaire is described in the non-prepublished patent application PCT/IB2008/052057. This LED luminaire comprises a light exit window, an array of LEDs positioned at the sides of the exit window and a reflective screen opposite the light exit window comprising both a specularly reflective part adjacent the light sources and a diffusely reflective part opposite the light exit window. The LEDs emit lambertian light into the direction of both reflective parts, aiming to transform the LED luminance from a very high and discrete degree to a uniform degree of brightness which is acceptable to the observer. Though said luminaire is an improvement in comparison with the known prior art, the described luminaire still has the drawback that it does not fully comply with the glare restrictions set by the EN12464 norm. Glare results from excessive contrast between bright and dark areas in the field of view. Another drawback is that light is still emitted through the light exit window directly by the specularly reflective part of the reflective screen, i.e. not via its diffusely reflective part, so that light source images still remain visible in the specularly reflective part and increase the risk of glare.